An electric vehicle, which includes an electric motor only as a driving source for traveling, is silent when traveling at low speeds. A hybrid vehicle, which includes an electric motor and an internal combustion engine as a driving source for traveling, is silent when travelling at low speeds by a driving force generated by the electric motor. Therefore, pedestrians and the like are less likely to notice approach of the vehicle.
To address the above issue, it has been known a vehicle approach notification device for such a silent vehicle that generates a notification sound to notify a pedestrian and the like of a presence of the vehicle. For example, JP-A-05-213112 discloses a vehicle approach notification device that generates a notification sound signal which has a frequency changing according to a vehicle speed, and emits a notification sound based on the notification sound signal to a periphery of a vehicle.
Also, it has been known to generate a pseudo engine sound or a pseudo motor sound, as the notification sound, by a synthetic sound (a chord sound) composed of a plurality of frequency components. Further, it has been known to change each frequency of the synthetic sound little by little according to the change of the vehicle speed so that a pedestrian and the like can recognize the speed of the vehicle. Such a technology is, for example, disclosed in JP-A-2012-17071.